Thank you for your reply. I have spent over a week searching for an answer regarding this question. After trying for a while to fix it, I ultimately factory reset the raspberry pi and redownloaded raspbian and the other softwares. Finally, I was able to get it to work after a complete reset.
oh...sorry I missed that. when I looked at the image, I saw the message under the node "node-red:pi-gpio.status.not-avaliable' and (foolishly) jumped to the conclusion they were using the rpi-gpio node.
Thank you for your reply. Regarding whether or not the HC-SR04 is 3.3V compatible, I'm not really sure. But I would assume it is probably the newer one and therefore should be 3.3V compatible, as I got it recently (2 months ago) at Micro Center (https://www.microcenter.com/product/613642/leo-sales-ltd-ultrasonic-sensor-module).
As mentioned in your linked tutorial I am using the same resistors and setup. A factory reset on the Raspberry Pi has solved the problem, although I never figured out the exact root of the issue. But all is good now that it is finally working.